1. Field of the Invention
The invention pertains to the field of automotive transmissions. More particularly, the invention pertains to an automotive transmission with orbital gearing and a variable sun gear control.
2. Description of Related Art
Known conventional transmissions use the vehicle's engine as the primary control for making changes in vehicle speed.
The manual transmission uses a clutch to change the gear ratio, with the engine being completely disconnected from the transmission momentarily during each level of gear change, and also with the engine being quickly revved up to fairly high rpm during each level change.
The standard automatic transmission uses a torque converter to avoid the complete disconnect of the engine between levels of gear ratio change, but the inefficiency of the torque converter causes considerable slippage between engine and transmission output, particularly during initial start-up and lower speeds when as much as 50% of the engine torque may be lost. This type of transmission blends engine and transmission better than the manual, but the engine still must be revved to higher rpm during each level of multiple gear change. Also, even during engine idle when the vehicle is stationary, the automatic transmission creates a constant loss of efficiency through hydraulic losses occurring in the torque converter.
The conventional acceleration rates for engine rpm during the revving for each gearing level in both manual and automatic transmissions is often between 1000-2000 rpm/sec, and this rapid acceleration of the engine's internal parts (crank shaft, pistons, valve cams) can result in a 20-25% loss in efficiency.
There have been many different forms of automatic infinitely-variable transmissions (“IVT”), in which usable torque is supplied to the drive wheels of the automotive vehicle through a continuum of constantly variable speeds. The IVT is distinguished from the continuously-variable transmission (“CVT”), in which vehicle speed is continuously changed throughout several successively-increasing speed and torque output levels. However, until recently, no IVT or CVT has been developed that is capable of successfully handling a full range of torque and engine sizes from a very small vehicle through a large commercial truck. Torvec, Inc., the assignee of the present invention, has recently successfully tested an IVT that can be readily sized to cover this entire range of engine size and torque requirements. Also, this recently tested IVT was specifically designed for propelling not only large SUVs (sport utility vehicles) but also small trucks and school busses. One of the latest designs of the Torvec IVT is disclosed in U.S. Pat. No. 6,748,817 entitled “Transmission with Minimal Orbiter”.
Torvec IVT's have been progressively improved during an extensive period of product testing, and a current design produces continuous changes of torque and speed from start-up through an overdrive ratio without any intermediate discontinuities while using engine acceleration rates of no more than 90-100 rpm/sec. These remarkable results are achieved with an apparatus that is significantly smaller and lighter than presently available conventional automotive transmissions.
The earlier Torvec IVT designs combined a variable hydraulic pump and a hydraulic motor with a gear orbiter to form an infinitely variable transmission so that, as the speed of the hydraulic motor increases the rotation of the gear orbiter, the output shaft speed increases and the speed of the vehicle increases. This basic design was recently significantly modified to operate in an unconventional manner. Namely, while the engine input was delivered to an input sun gear of the orbiting gear complex, the changes in output gear ratios were obtained by using the combined operation of the variable hydraulic pump and motor to slow the rotation of the web so that, as the rotation of the web in the direction of the engine was slowed, the transmission produced a continuously decreasing gear reduction, and, when the web was brought to a stop, the transmission provided an overdrive ratio of the engine input.
The recent Torvec transmissions just discussed above increase transmission efficiency by using a hydraulic pump and motor combination, rather than the vehicle engine, as a primary control of vehicle speed, thereby avoiding the above-mentioned engine acceleration losses. However, these recent Torvec transmissions still lose efficiency through the split torque path that delivers torque to the hydraulic pump and motor.
As just indicated above, when accelerating a vehicle with both manual and automatic transmissions, the revving of the engine, far exceeding 2,000 rpm, during various gear change levels is an inefficient use of horsepower. Even the relatively new Torvec IVT transmissions are burdened with the inefficient use of horsepower that arises from the division of a portion of the vehicle engine output into a split path for driving the transmission's hydraulics.
Special attention is also called to another prior art apparatus, namely, the Torvec long-piston hydraulic machines disclosed in U.S. Pat. No. 6,983,680 and U.S. 2004/0168567, which are hereby incorporated herein by reference. This special prior art is referred to in greater detail in the Summary portion below.
The invention disclosed herein is a further improvement of the successfully-tested earlier versions of the Torvec IVT just discussed above, and the hydraulic machine in the disclosed preferred embodiment utilizes a variation of the hydraulic machine disclosed in U.S. Pat. No. 6,983,680 and U.S. 2004/0168567.